基于透明土材料的扩底楔形桩中性点位置测定模型试验与分析

摘要

扩底楔形桩由于其桩身截面倒楔形结构，可以有效降低负摩阻力对基桩的影响；但是倒楔形面和扩大头的存在对中性点位置的影响却尚不清楚。为了分析扩底楔形桩中纵向截面形式（倒楔形面和扩大头）变化对基桩中性点位置的影响规律；基于透明土材料和数字图像处理PIV（ particle image velocimetry ）技术，采用非插入式测试方法开展地面堆载作用下扩底楔形桩的中性点位置测定模型试验，测得不同地面堆载等级作用下桩体沉降与桩周土体沉降等变化规律，探讨桩-土相对位移和中性点位置随地面荷载等级的变化规律；同时进行了负摩阻力作用下等截面桩中性点位置测定透明土模型试验作为对比分析。研究结果表明，利用透明土材料来研究扩底楔形桩中性点位置的试验方法在技术上是可行的。所研究试验条件下，由于倒楔形面和扩大头的存在，扩底楔形桩的中性点位置明显较常规等截面桩低。%The negative skin friction of belled wedge pile can be reduced by inverted wedge cross -section.How-ever, the neutral point position whether will be reduced because of inverted wedge cross -section is unknown .In or-der to analysis the neutral point position influenced by longitudinal cross -section form ( inverted wedge surface and enlarged pile base ) changing , the model test on neutral point position of belled wedge pile was carried out by using transparent soil material and digital image processing PIV ( particle image velocimetry ) technology .The pile and layered soil settlement under different surcharge loads were non-intrusive measured .The pile-soil relative displace-ment and neutral point position versus surcharge loads were analyzed and discussed .In the same time , model test on neutral point position of traditional equal section pile under negative skin friction was taken out for comparative analysis .The results show that transparent soil material is technically feasible for study the neutral point position of piles problems.The results also show that the neutral point position of belled wedge pile is obviously lower than that of traditional equal section pile because of inverted wedge surface and enlarged pile base in this model test condi -tion.